The current development towards truly mobile computing and networking has brought on the evolvement of various access technologies, which also provide the users with access to the Internet when they are outside their own home network. The first public communication network that provides a truly ubiquitous World Wide Web (WWW) access is the GSM-based mobile telephone network.
So far, the use of the Internet has been dominated by person-to-machine communications, i.e. information services. The evolution towards so-called third generation (3G) wireless networks brings along mobile multimedia communications, which will also change the way IP-based services are utilized in public mobile networks.
The new multimedia capable mobile terminals (multimedia phones) provide an open development platform for application developers, allowing independent application developers to design new services and applications for the multimedia environment. The users may, in turn, download new content, such as music or software, to their mobile terminals and use them therein. Therefore, a mechanism is also required in the network for protecting the rights of the content owners and for preventing illegal use of the content.
Digital Rights Management (DRM) is a technology developed by the Open Mobile Alliance (OMA) for securing, selling, and distributing digital content in a mobile environment. In the first DRM specification, the system includes three levels of functionality, which are termed forward lock, combined delivery, and separate delivery. In forward lock, a hard-coded feature in the terminal prevents the user from copying or forwarding the content downloaded in the terminal. Typical present-day downloadable content, such as ringing tones or logos, is protected by the forward lock mechanism. In combined delivery, a rights definition, termed rights object, is added to the DRM message delivered to a terminal. The DRM message thus includes two elements: the content and the rights object. The rights object defines permissions and constraints for the usage of the content, such as the number of days or the number of times the content may be used. The combined delivery also utilizes forward lock: neither the content nor the rights object can be forwarded after they have been downloaded to a terminal. In separate delivery, which is intended to protect higher value content, the content and the rights object may be delivered separately. The content is encrypted into so-called DRM Content Format (DCF) and the rights object contains a key (CEK, Content Encryption Key) for decrypting the content in the terminal. The content may thus be delivered through an insecure channel, while a more secure channel is used to deliver the rights object. Typically, Wireless Application Protocol (WAP) push is used to deliver the rights object via Short Message Service (SMS).
The separate delivery enables so-called super-distribution, which allows the content, but not the rights object, to be forwarded to another terminal. When the content is to be forwarded, metadata including location information of the application server of the issuer of the rights is inserted in the DCF object to be forwarded. The terminal receiving the DCF object, i.e. the content, contacts the application server by opening a browsing session, which allows the user to choose the kind of rights he or she desires. The rights object with the key required for decrypting the content is then delivered through a secure channel to the terminal.
A drawback related to the current DRM mechanism is its inflexibility as to the management of the rights. Although content may be delivered to other users, the rights objects remain locked in the terminal, and a new rights object has to be acquired, even though the user delivering the content would be willing to give up the rights too. As there is no mechanism for forwarding the rights, some of the rights already acquired may remain unconsumed for good.
The present invention seeks to eliminate the above-described drawback and to improve the flexibility of the DRM system.